The present invention is directed to the field of envelopes, and is more specifically directed to envelopes having tear strips or tear-off flap portions or tamper-evident flap portions specifically formed therein.
It is known to make envelopes from a number of different kinds of paper stocks. In recent years, envelopes have been made from spun olefin in the form of heat and pressure high-density polyethylene fibers forming a sheet. The spun bonded olefin is sold by E.I. Du Pont under the trademark TYVEK, and envelopes formed of TYVEK have been sold by Atlantic Envelope Company under the trademark POLYWOVE. The popularity of such envelopes is due in large part to the light weight, high dimensional stability and capacity, great toughness and durability, and low absorption of water of such envelopes. However, the excellent stability, thoroughness and durability characteristics of high-density polyethylene fiber envelopes make them extremely difficult to open because they are highly resistant to tearing, and the strength of the adhesive necessary to bond the flap to the body of the envelope necessitates substantial effort to separate the flap from the body of the envelope once it has been sealed. Such are the characteristics of these envelopes that it is even difficult to open them at the fold line of the flap using a conventional letter opener. It is therefore often necessary to resort to using scissors to cut open the envelope at the top or bottom. However, in doing this, there is often considerable risk or also cutting, and therefore damaging, the contents of the envelope.
The characteristics of these envelopes which make them popular for business use also make them susceptible to undetected tampering. In an increasingly common practice, an envelope is intercepted after leaving the sender, one of the flaps is carefully opened, materials are added or removed, the envelope is resealed and replaced, and in the case of added materials, before being delivered to its destination, the envelope is intercepted, reopened, relieved of the added materials, and resealed. Because of its dimensional stability, toughness, and durability, the envelope can be opened, resealed, reopened, and again resealed at the flap without any outward signs which would alert the intended recipient. Tampering is therefore difficult, if not impossible, to detect. The substantial effort needed to open the flaps, far from being a deterrent, is in fact a kind of incentive, as it falsely leads both the sender and the intended recipient to assume that the envelope is tamper-proof.
Until the present invention, there had been no satisfactory mechanism incorporated into bonded, high-density polyethylene fiber envelopes to enable them to be easily opened or to provide evidence of tampering. I have discovered that ultrasonic energy can be applied to sheets of bonded, high-density polyethylene fibers to form distress patterns at which the fibers are weakened and to provide either a tear strip which can be pulled away from the remainder of the envelope to create an opening in the envelope. I have also discovered that ultrasonic energy can be applied to the seal flap and other closure locations of envelope blanks formed of sheets of bonded, high-density polyethylene fibers to form distress patterns or lines which will function as a tamper-evident feature. Moreover, the inventive method can also be used to create tear strips or tamper-evident strips in envelopes made from standard paper stock, and to create tear-off portions in the flaps of envelopes.
The following documents disclose apparatus for applying ultrasonic energy to plastic or thermoplastic material to emboss designs in the materials, or to fuse them together, or to form a crease in them: U.S. Pat. No. 4,529,473 to Mims; U.S. Pat. No. 4,389,267 to Denslow; U.S. Pat. Nos. 4,326,903 and 4,265,847 to Summo; U.S. Pat. No. 4,247,273 to Pogrzeba et al.; U.S. Pat. No. 4,237,181 to Tanabe et al; U.S. Pat. No. 4,071,853 to Kuris; U.S. Pat. No. 4,032,382 to Obeda; U.S. Pat. No. 3,893,532 to McDonald et al.; U.S. Pat. No. 3,752,620 to Renoux; U.S. Pat. No. 3,749,620 to Montgomery; U.S. Pat. No. 3,635,609 to Balamuth; U.S. Pat. No. 3,483,066 to Harris et al.; U.S. Pat. No. 3,440,117 to Soloff; U.S. Pat. No. 3,224,916 to Soloff et al.; and Data Sheets PW-31 and FF-2 of Branson Sonic Power Company. However none of these documents disclose or suggest the use or ultrasonic energy to form distress lines defining a tear strip or tear-off portion for use in an envelope of any kind, or the use of ultrasonic energy to form distress line areas defining a tear strip or tear-off portion or to form distress patterns defining a tamper-evident feature in bonded, high-density polyethylene fibers for use in an envelope or for any other purpose.